1. Field of the Invention
The present invention relates generally to the design and use of medical devices. More particularly, the present invention relates to a method and apparatus for accessing an implanted port.
Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for applications, such as intravenous feeding, intravenous drug delivery, and other applications which are limited in time, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For long-term vascular access suitable for hemodialysis, hemofiltration, and the like, the most common approach is to create a subcutaneous arteriovenous (A-V) fistula. The fistula is preferably created by anastomosing an artery, usually the radial artery, to a vein, usually the cephalic vein. The vein dilates and eventually arterializes, becoming suitable for repeated puncture using a needle for access. A-V fistulas may also be created using autologous or heterologous veins, by implanting synthetic blood vessels, typically PTFE tubes, and the like.
The needles used for percutaneously accessing an A-V fistula are large bore coring needles, often referred to as fistula needles. The needles have a bore diameter of 1.49 mm or larger, and permit the high blood flow rates needed for hemodialysis, hemofiltration, and other extracorporeal procedures. One technique for repeatedly accessing an A-V fistula is referred to as the "button hole" technique. Such technique relies on repeatedly accessing the fistula through the same tissue tract, eventually creating a non-healing channel through the tissue overlying the fistula. The channel is lined with scar tissue which forms over time. While generally successful, the button hole technique results in significant bleeding everytime the fistula needle is removed after a treatment is completed. The bleeding, in turn, causes scabbing, and the scab must be removed prior to subsequent needle insertion in order to avoid the risk of pushing scab into the fistula. The removal of the scab causes patient discomfort and bleeding and increases the risk of infection.
As an alternative to the use of an A-V fistula, a variety of implantable ports have been proposed over the years for use in hemodialysis, hemofiltration, and other extracorporeal treatments. Typically, the port includes a chamber having an access region, such as a septum, where the chamber is attached to an implanted cannula which in turn is secured to a blood vessel. In the case of veins, the cannula is typically indwelling, and in the case of arteries, the cannula may be attached by conventional surgical technique.
Percutaneous access to a port through a septum, however, is generally limited to small diameter, non-coring needles. Large diameter needles will core the septum, i.e. form permanent channels therethrough, which will destroy the septum after repeated uses. Small diameter, non-coring needles will remove little or no material from the septum, allowing it to close after the needle is removed. While small needles will thus preserve the septum, they are generally incompatible with the high flow rates which are used with hemodialysis and other extracorporeal treatments.
Implantable ports having an access aperture and internal valve mechanism for isolating the implanted cannula have also been proposed. One type of implantable valved port is described in a series of issued of U.S. patents which name William Ensminger as inventor. The Ensminger access ports have internal lumens for receiving a percutaneously introduced needle and an internal valve structure for isolating the port from an associated implanted cannula. Generally, the Ensminger ports have a needle-receiving aperture which is oriented at an inclined angle relative to the patient's skin. The Ensminger patents do not describe port access using large diameter, coring needles, such as fistula needles. Moreover, as many of the specific Ensminger designs employ elastomeric valve elements, it is likely that the valve mechanisms would be damaged if the ports were accessed by a fistula needle or other large bore coring needle. Representative Ensminger patents are listed in the Description of the Background Art below.
For these reasons, it would be desirable to provide improved methods and apparatus for percutaneously accessing subcutaneously implanted ports. Such methods should reduce patient trauma, provide for reliable access to the implanted port, minimize the risk of infection to the patient, and preferably require only minor modifications to present port implantation procedures. In particular, it would be desirable to provide methods and apparatus for establishing high volume access to subcutaneously implanted ports having valve mechanisms, using large diameter needles, such as conventional fistula needles. Such percutaneous access should accommodate repeated needle penetrations through the same tissue location overlying an aperture of the access port. At least some of these objectives will be met by the invention described hereinafter.
2. Description of the Background Art
U.S. Pat. No. 5,562,617 and WO 95/19200, assigned to the assignee of the present application, describe implantable vascular access systems comprising an access port having an internal slit or duck bill valve for preventing back flow into the port. Vascular access ports having various articulating valves for isolating the port from the vascular system in the absence of external percutaneous connection to the port are described in the following U.S. patents which name William Ensminger as an inventor: 5,527,278; 5,527,277; 5,520,643; 5,503,630; 5,476,451; 5,417,656; 5,350,360; 5,281,199; 5,263,930; 5,226,879; 5,180,365; 5,057,084; and 5,053,013. Other patents and published applications which show implantable ports having valve structures opened by insertion of a needle include U.S. Pat. Nos. 4,569,675; 4,534,759; 4,181,132 and WO 96/31246.